1,721,630 research outputs found
A never-ending story in the sky: The secrets of chemical evolution
Full text linkCosmic evolution is the tale of progressive transition from simplicity to complexity. The newborn universe started with the simplest atoms formed after the Big Bang and proceeded toward the formation of the so-called ‘astronomical complex organic molecules’ (aCOMs), most of them showing a clear prebiotic character. Understanding the chemical evolution of the universe is one of the main aims of Astrochemistry, with the starting point being the knowledge whether a molecule is present in the astronomical environment under consideration and, if so, its abundance. However, the interpretation of astronomical detections and the identification of molecules are not at all straightforward. Indeed, the extraterrestrial chemical inventory has been obtained by means of astronomical observations based on spectroscopic signatures determined in laboratory (either experimental or computational) studies. Even though the presence of aCOMs has been known for decades, the processes that lead to their synthesis are still hotly debated or even unknown. It is often assumed that aCOMs are mostly synthesized on grain surfaces during the so-called warm-up phase, when various radicals trapped in the grain mantles acquire mobility and recombine into large molecules. However, recent detections of aCOMs in cold environments have challenged this exclusive role of grain-surface chemistry. Clearly, gas-phase chemistry is at work in cold environments. Moving to Titan's atmosphere, prior to the Cassini-Huygens arrival in the Saturn system, it was generally believed that Earth and interstellar space are the two places where organic molecules are/were synthesized extensively. However, the experimental measurements by the instruments on board the Cassini orbiter spacecraft and the Huygens probe lander have changed this view. To disclose the “secrets” of chemical evolution across space, the first step is the understanding of how small prebiotic species are formed and how the chemical complexity can further increase. This review indeed addresses the chemical evolution in space, focusing – in particular – on the role played by molecular spectroscopy and quantum-chemical computations. To summarize, in this review we will first of all present how the signatures of molecules can be found in space. Then, we will address, from a computational point of view, the derivation of the molecular spectroscopic features, the investigation of gas-phase formation routes of prebiotic species in the ISM, and the evolution of chemical complexity, from small molecules to haze, in Titan's atmosphere. Finally, an integrated strategy, also involving high-performance computers and virtual reality, will be discussed
The Persico equation for minimum uncertainty states
Full text linkWe present an important and forgotten result of fundamental quantum mechanics obtained in 1930 by Enrico Persico, consisting of an eigenvalue equation for minimum uncertainty states
Interpretability meets accuracy in computational spectroscopy: The virtual multifrequency spectrometer
No full textThe virtual multifrequency spectrometer (VMS) integrates state-of-the-art computational implementations of different spectroscopies with a powerful graphical user interface, which offers an invaluable aid in preorganizing and displaying the computed spectroscopic information. This chapter provides an overview of the VMS software, thus focusing on its peculiarities and unique features. It presents a short introduction of the theoretical background for the selected spectroscopies and of the corresponding quantum chemical requirements. The chapter also presents the current status of VMS in some detail with specific reference to rotational, vibrational, vibronic, and magnetic spectroscopy. To address the great potentialities of the VMS software, various case studies have been selected. The choice has been made in order not only to point out the ability of VMS in dealing with different spectroscopic techniques and thus providing an exhaustive characterization but also to demonstrate the scientific impact of VMS in the field
Gas-Phase Computational Spectroscopy: The Challenge of the Molecular Bricks of Life
Full text linkGas-phase molecular spectroscopy is a natural playground for accurate quantum-chemical computations. However, the molecular bricks of life (e.g., DNA bases or amino acids) are challenging systems because of the unfavorable scaling of quantum-chemical models with the molecular size (active electrons) and/or the presence of large-amplitude internal motions. From the theoretical point of view, both aspects prevent the brute-force use of very accurate but very expensive state-of-the-art quantum-chemical methodologies. From the experimental point of view, both features lead to congested gas-phase spectra, whose assignment and interpretation are not at all straightforward. Based on these premises, this review focuses on the current status and perspectives of the fully a priori prediction of the spectral signatures of medium-sized molecules (containing up to two dozen atoms) in the gas phase with special reference to rotational and vibrational spectroscopies of some representative molecular bricks of life
Collisional broadening and hyperfine structure of rotational transitions. Reply to the comments on “A never-ending story in the sky: The secrets of chemical evolution”
Full text linkWe would like to thank all commentators for their insightful comments, all of them contributing to enrich and complement our review. Among them, the comments by Agúndez -Cernicharo [1], Hochlaf [2], and Feng -Gou [3] provided the opportunity to further extend the discussion
The challenging playground of astrochemistry: An integrated rotational spectroscopy-quantum chemistry strategy
Full text linkWhile it is now well demonstrated that the interstellar medium (ISM) is characterized by a diverse and complex chemistry, a significant number of features in radioastronomical spectra are still unassigned and call for new laboratory efforts, which are increasingly based on integrated experimental and computational strategies. In parallel, the identification of an increasing number of molecules containing more than five atoms and at least one carbon atom (the so-called "interstellar" complex organic molecules), which can play a relevant role in the chemistry of life, raises the additional issue of how these species can be produced in the typical harsh conditions of the ISM. On these grounds, this perspective aims to present an integrated rotational spectroscopy-quantum chemistry approach for supporting radioastronomical observations and a computational strategy for contributing to the elucidation of chemical reactivity in the interstellar space
- …
